if I remember correctly the pads are note numbers and the color is defined by velocity.
what you need is something like a flipflop relay, so a noteON triggers a neverending noteON for launchpad (without sending a noteOFF). if you press a launchpad key again launchpad receives a noteOFF.

I am not terribly aware of graphical environments for stuff like that. probably Synthedit with some custom modules. did some launchpad stuff with Sensomusic Usine and its integrated script host.

either way, this is very possible. Assumedly you have a midi-out running FROM ableton back to the LP in the preferences?

If so - one way to do this - when you hit the key, the launchpad sends the note back to itself, to light the LED.

If (parameter)= 0, then parameter= 127

if parameter= 127, then parameter=0

(that syntax is all wrong, but you see - when you press it, if it is already on (127 velocity), it switches off (0 velocity), and vice versa.

alternately, you assign a global parameter to the velocity of the outgoing note (what goes FROM LP to ableton), then when you add the code for the feedback to the LP, just grab this variable and use it as the velocity.

i can find proper code if i havent been able to explain that well enough.